1. Field of the Invention
The present invention relates to an apparatus for recording information and a method for retracting the head, in particular, an information recording apparatus for recording and/or reproducing by moving the head with respect to a recording medium, and a method for retracting the head.
2. Description of the Prior Art
In prior art optomagnetic disk devices, a distance between an object lens and a disk at the focused position, that is, a working distance of approx. 1 mm has been secured. Therefore, the distance had comparatively sufficient allowance, wherein since a stopper mechanism could be provided between the object lens and the disk, it was possible to physically prevent both of these from being brought into contact with each other. Therefore, it was not necessary for the object lens to be retracted from the disk to a position separated therefrom.
FIG. 1 is a perspective view showing one example of a movable head of a prior art optical disk device, and FIG. 2 is a sectional view showing one example of a movable head of a prior art optical disk device.
The movable head 200 is caused to be movable in the directions of the arrows B-B′, that is, in the diametrical directions of an optical disk 202 by a voice coil motor 201.
The movable head 200 is composed so as to include a lens holder 203, a plate spring 204, a focus coil 205, an object lens 206, an erect mirror 207, a movable head body 208, and a permanent magnet 209. The object lens 206 is fixed on the lens holder 203. Also, the lens holder 203 is fixed on the movable head body 208 via the plate spring 204 and is caused to be swingable in the directions of the arrows A-A′ with respect to the movable head body 208. The focus coil 205 is attached to the side of the lens holder 203. The permanent magnet 209 is fixed on the side of the movable head body 208, which faces the focus coil 205.
As a drive current is caused to flow into the focus coil 205, a current flowing in the focus coil 205 and a magnetic field that is generated by the permanent magnet 209 interact with each other, wherein a force is generated at the focus coil 205, and it is possible to cause the lens holder 203 to sway in the directions of the arrows A-A′ by an electromagnetic force acting on the focus coil 205. Since the lens holder 203 is caused to sway in the directions of the arrows A-A′, the object lens 206 is accordingly caused to sway in the directions of the arrows A-A′, thereby enabling focusing.
Also, the erect mirror 207 is disposed under the object lens 206 of the movable head body 208 and is fixed on the movable head body 208. A light beam L is made incident from a fixed head (not illustrated) into the erect mirror 207. The erect mirror 207 reflects the light beam L input from the fixed head to the direction of the object lens 206, that is, to the direction of the arrow A. The light beam L reflected by the erect mirror 207 is provided into the object lens 206. The object lens 206 converges the light beam L from the erect mirror 207 and provides the same to the optical disk 202.
The light beam L that is provided into the optical disk 202 is reflected by the optical disk 202, and is provided to the erect mirror 207 through the object lens 206 again. The erect mirror 207 reflects the light beam L input from the object lens 206 to the direction of the fixed head, that is, the direction of the arrow B.
At this time, in order to prevent the object lens 206 and the disk 202 from colliding with each other due to an impact applied from the outside, a stopper mechanism 210 that controls movement of the lens holder 203 in the direction of the arrow A is provided.
In order to provide the stopper mechanism 210, it is generally necessary to secure a working distance d of 0.5 mm or the like in the worst case to absorb a dimensional error of components and an assembling error of the apparatus. However, recently, it has been requested that the diameter of the light beam L be made smaller in line with an increase in the recording density of the disk 202. In order to achieve a smaller diameter of the light beam L, it is necessary that the working distance d be made smaller. However, as the working distance d becomes smaller, there may caused a possibility for the disk 202 and the object lens 206 to collide with each other due to a facial swaying of the disk 202.
Therefore, without depending on the stopper mechanism 210, it is necessary to provide a mechanism for retracting the object lens 206 by using auxiliary power.
As a method for retracting the object lens 206 by using auxiliary power without depending on the stopper mechanism 210, some methods have been taken into consideration, one of which is a method for employing a battery driven by a chemical reaction as auxiliary power for retraction, and the other of which is a method for employing a back electromotive force of a motor due to inertia rotations of a disk as auxiliary power as in Japanese Unexamined Patent Application No. 1992-32029.
However, the life cycle of charging and discharging is shortened to be several hundred times where, in order to secure retraction power, a battery employing chemical reaction such as a lithium ion battery is provided. Also, there is another problem in that a longer period of time is required to charge the battery. Therefore, it is unsuitable to use a battery employing chemical reaction as power for retraction of an optical disk device.
Further, as in Japanese Unexamined Patent Application 1992-32029, in the method for utilizing a back electromotive force of a motor, which is induced by inertia rotations of a disk, as power for retraction, voltage that can be picked up depends on the number of revolutions of the disk. That is, although a high voltage can be picked up where the disk is rotating at a high speed, only a low voltage can be obtained where the disk is rotating at a low speed, wherein another problem arises in that sufficient power for retraction cannot be provided to an actuator.
Usually, since the surface of the disk is not completely flat but is distorted in the range of several tens of micrometers to several hundreds of micrometers, the lens actuator always repeats up and down movements and focuses with respect to the rotating disk. Therefore, unless a sufficient retraction current is caused to flow, there is a danger that the lens may be brought into collision with the disk due to inertia. Also, where an impact is provided from the outside during the retraction, an adequate acceleration rate is not provided to stand against the impact, and there may be a danger of a collision.